Aspects and embodiments of the invention are directed to range-finding apparatus, methods, and applications thereof. More particularly, aspects and embodiments are directed to lidar and optical scanning apparatus, methods, and applications and, most particularly to range-finder apparatus having a wide field of view, associated methods, and applications thereof.
Mapping the distance to objects by measuring a time of flight has become one of the main sensing schemes for the purpose of improving the safety of automotive transportation and autonomously driven vehicles. Distances to objects, such as cars, pedestrians, and obstacles may be measured, for example, over a 360 degree field of view with sub one (1) degree resolution and a 10 fps frame rate by launching a nano-second pulse from a laser toward an object. The reflected light from the object is detected by a detector, comprising for example, a silicon photo diode or an avalanche photo diode (APD). The distance between the light source and the object is measured by detecting the delay between the launching of the pulse by the laser and the arrival of the echo at the detector. Such a distance measurement system used along with object recognition can be used to reduce the probability of car accidents.
Also, autonomous driving requires some range finding mechanism such as laser range finding. Laser range finding is also of interest for consumer applications, such as robot cleaners and others. Mapping of objects in a room, for example, by a distance measurement increases the area throughout the room that can be cleaned by providing additional information to the existing routing algorithm.
A new generation of Lidar systems with high resolution, high ranging accurate, and high frame rate is heading toward the direction of miniaturization, light weight, portability, and low cost and has been applied widely in the civilian and military fields such as laser ranging, topography, architectural drawing, environmental monitoring, vehicle driving navigation, unmanned ground vehicle navigation, etc. In Lidar systems, a resonant scanner can be considered one of the important components because of its huge advantages, including fast scanning speed, flexibility, low power consumption, etc. However, the mechanical tilt angle of a resonant scanner with a small aperture of 10 mm×6 mm has a maximum optical full scan angle of only about 50°, which is simply not enough for a Lidar system for autonomous applications.
For automotive applications, a light detection and ranging (lidar) system is currently relatively expensive. For example a Lidar system currently offered by Verodyne has been found to cost about $80,000. The system employs conventional mechanical scanning; that is, both the laser sources and the detectors are mounted on a rotating mechanical mount. Pulsed light from the laser is collimated by a lens and directed toward an object, and an echo of the pulse coming off the object is captured by detector optics and focused on the detector, while the entire optical setup is rotating at a high speed. This mechanical scanning approach is believed to be the most effective mechanical scanning approach currently available. Since the light is collimated, the laser power density at the object is high, thus the reflected signal can be detected with a high signal-to-noise ratio (SNR).
In low cost car and various consumer applications, non-mechanical scanning is ideal to avoid failure of the scanning mechanism carrying the transmitter and the receiver. For this case, a rotating polygon mirror may be used to scan a laser across a scene, or a flood illumination array of laser diodes (LDs) or light emitting diodes (LEDs) can provide non-mechanical scanning. However for receiver optics, there is no viable solution available to map distance and angular position of an object other than low resolution avalanche photo diode (APD) arrays whose resolution is very low compared to the desired specifications of 10 fps, 360 degree FOV, and sub one (1) degree resolution.
Advantages and benefits over the current state of the art as well as solutions to problems associated with current state of the art apparatus and methods, appreciated by those skilled in the art, would be realized by improved range-finding and scanning apparatus and methods as enabled by the embodiments disclosed and claimed herein, particularly by the elimination of bulky mechanical scanning apparatus, increased field of view, and improved resolution of measurement data.